1. Technical Field
The present invention relates to orthopedic surgery, and in particular to devices for stabilizing and fixing the bones and joints of the body. Particularly, the present invention relates to a spinal fixation system that includes surgical instruments that can be used for locking or unlocking a taper lock screw, the screw preferably being multi-planar and useful for securing a spinal rod or plate to a vertebra.
2. Background Art
The spinal column is a complex system of bones and connective tissues that provides support for the human body and protection for the spinal cord and nerves. The adult spine is comprised of 24 vertebral bodies, which are subdivided into three areas including seven cervical vertebrae, 12 thoracic vertebrae and five lumbar vertebrae. Between each vertebral body is an intervertebral disc that cushions and dampens the various translational and rotational forces exerted on the spinal column.
There are various disorders, diseases and types of injury which the spinal column may experience in a lifetime. The problems may include but are not limited to scoliosis, kyphosis, excessive lordosis, spondylolisthesis, slipped or ruptured discs, degenerative disc disease, vertebral body fracture, and tumors. Persons suffering from any of the above conditions typically experience extreme or debilitating pain and often times diminished nerve function.
One of the more common solutions to any of the above mentioned conditions involves a surgical procedure known as spinal fusion. A spinal fusion procedure involves fusing two or more vertebral bodies in order to eliminate motion at the intervertebral disc or joint. To achieve this, natural or artificial bone, along with a spacing device, replaces part or all of the intervertebral disc to form a rigid column of bone and mechanical hardware. In this way damaged or diseased vertebrae are connected to healthy adjacent vertebrae to stabilize the spine while the bone grows and fusion takes place.
The mechanical hardware used to immobilize the spinal column typically involves a series of bone screws and metal rods or plates. When the spine surgery is posteriorly performed, it is common practice to place bone screws into the vertebral bodies and then connect a metal rod between the bone screws thus creating a rigid structure between adjacent vertebral bodies. When the spine surgery is performed anteriorly, it is common practice to attach a thin metal plate directly to the vertebral bodies and secure it to each vertebral level using one or more bone screws.
Many conventional devices for locking a spinal rod to a fixation hook or screw do not offer the needed variability to allow the spinal rod to be easily connected to adjacent vertebrae, which are not aligned on the same plane. In some cases the use of these devices may be permanently implanted in the subject. In other cases, the devices may be implanted only as a temporary means of stabilizing or fixing the bones or bone fragments, with subsequent removal when no longer needed. It is also common that device implants that were intended to be permanent may require subsequent procedures or revisions as the dynamics of the subject's condition warrant. For these reasons, it is desirable that an implanted device be provided, which can be easily locked and unlocked as desired by the surgeon.
In recent years some effort has been made to provide taper lock bone screws and further to provide taper lock bone screws that are multi-planar; however, even when multi-planar type bone screws have been developed, the use of those screws has proven difficult because the locking and unlocking instruments that are used by the surgeon during the surgical procedure are of a generic design and inadequate to quickly lock or unlock the bone screws. In addition, with prior conventional screws the mode of locking the screw and rod typically involves set screws or nuts, the application and tightening of which generates twisting or torsional forces, i.e., torque, which are transmitted through the screw to the bone to which the screw has been inserted. Such torsional forces can alter the disposition of the screw in the bone or can damage the bone, which may be of poor strength or quality in patients undergoing surgery. As such, the torsional forces can adversely affect the outcome of the procedure.
To meet the problem of securely connecting adjacent vertebrae, not on a common plane, a requirement exists to provide a multi-planar, taper lock screw that can be easily inserted and easily removed from the vertebral bone as desired and to provide the specialized instrumentation that can facilitate quick locking and unlocking of such a screw. It is also desirable that such a screw and the instrumentation for locking and unlocking the screw be configured so that the screw can be locked into position in relation to the bone and the spinal rod without the need to exert any additional torque to the screw. Additionally, the development of such a multi-planar screw and the locking and unlocking instrumentation can be designed so as to eliminate the need for an additional locking piece, such as the conventional, often difficult to manipulate set screw or nut that is a small separate element from the bone screw and normally requires threading with the application of torque onto the screw.
Conventional efforts to meet this need have fallen short in that no systematic approach has been provided that adapts the spinal rod to the multi-planar environment of the spine by using a multi-planar locking bone screw with specifically designed locking and unlocking instruments that present a quick, torqueless method of locking and unlocking the rod to the screw. Thus, while much attention is generally given to developing improved implants, the benefits of the innovations are often not fully realized because the appropriate instrumentation is not developed in a parallel systemic fashion.
For this reason, a major challenge of spine surgery is in the development of surgical instruments or instrumentation, for the surgeon to use during the implantation of the mechanical fixating structure. The instrumentation must be easy to use, effective, durable and most importantly, must not interfere with or cause further damage to the patient's anatomy.
While surgical instrumentation can sometimes be generic and effectively used in a variety of procedures, it is becoming more prevalent that the instrumentation is designed to be part of a specific system or procedure; that is, the instrumentation is designed to work best with certain implants.
Often implants are difficult to access and grasp with instruments thus increasing the surgeon's workload and prolonging the amount of time that the patient is in surgery. As improvements are made in the spinal implants themselves, it is often found that existing or generic instruments are inadequate to the task of effectively and efficiently manipulating the spinal implant. This is particularly troublesome when attempting to reduce a spinal rod into a receiving portion of an implant such as a pedicle screw or attempting to later release the spinal rod from that screw.
For these reasons there remains a need for a device which, in one simple action such as squeezing a lever, can reduce a posteriorly introduced rod into a pedicle screw and securely lock the rod into the pedicle screw. Conversely, there remains a need for a similar device which, through an equally simple action, can unlock a pedicle screw thereby releasing the posteriorly introduced rod.